The Receiver Domain of Hybrid Histidine Kinase VirA: an Enhancing Factor for vir Gene Expression in Agrobacterium tumefaciens

Abstract

The plant pathogen Agrobacterium tumefaciens expresses virulence (vir) genes in response to chemical signals found at the site of a plant wound. VirA, a hybrid histidine kinase, and its cognate response regulator, VirG, regulate vir gene expression. The receiver domain at the carboxyl end of VirA has been described as an inhibitory element because its removal increased vir gene expression relative to that of full-length VirA. However, experiments that characterized the receiver region as an inhibitory element were performed in the presence of constitutively expressed virG. We show here that VirA's receiver domain is an activating factor if virG is expressed from its native promoter on the Ti plasmid. When virA⌬R was expressed from a multicopy plasmid, both sugar and the phenolic inducer were essential for vir gene expression. Replacement of wild-type virA on pTi with virA⌬R precluded vir gene induction, and the cells did not accumulate VirG or induce transcription of a virG-lacZ fusion in response to acetosyringone. These phenotypes were corrected if the virG copy number was increased. In addition, we show that the VirA receiver domain can interact with the VirG DNA-binding domain.

The Integrity of the Periplasmic Domain of the VirA Sensor Kinase Is Critical for Optimal Coordination of the Virulence Signal Response inAgrobacterium tumefaciens

“…3B). The data best fit a monomer-dimer model with a K d (dissociation constant) of 39.8 M, providing additional evidence that the periplasmic domain can dimerize by itself (15), has recently been found to have a positive regulatory effect on VirA kinase activity (72). (B) Predicted secondary structure of the N-terminal region of wild-type VirA.…”

The Family Rhizobiaceae

“…The release and transfer of T-DNA into the plant genome occurs through a diverse class of virulence genes (vir). Plant phenolic compounds such as p-hydroxybenzoic acid and vanillin induce the expression of the vir genes (Maury et al 2010;Wise et al 2010).…”

Engineering robust control of two-component system phosphotransfer using modular scaffolds

“…The degree to which the local concentration controls flux in the scaffolded pathways of higher organisms is unclear, but the frequency of enzyme coassembly suggests it does play a significant role. Interestingly, recent work also has identified HKs containing domains responsible for binding RRs that may play a role in determining kinase specificity (20,21). In this work we replace several native TCSs with components that have been translationally fused to protein-protein interaction domains and peptide ligands, so that expression of synthetic scaffolds can be used specifically to colocalize noncognate components for the purpose of directing phosphotransfer in vivo.…”